Patent Document 1 describes an interior permanent magnet rotor formed of a rotor core in which a plurality of permanent magnets are embedded at predetermined intervals. In Patent Document 1, in a cross section perpendicular to a central axis of rotation, the rotor has protruding portions formed on an outer peripheral face thereof, the protruding portions each opposing the vicinity of a central portion of each permanent magnet and having an arc-shaped cross section protruding outward. With the rotor having such a configuration, the distance between the rotor and a stator is maximized in the vicinity of magnetic pole end portions of the rotor, which makes it difficult for magnetic flux to pass through such areas. Thus, magnetic flux generated by each permanent magnet can be linked effectively with the stator, and a decrease in electromotive force can therefore be prevented. Moreover, with the rotor having the above-described configuration, the distribution of magnetic flux density generated by the rotor can be approximated to a sinusoidal waveform. Thus, during rotation, magnetic flux linked with the stator can be smoothly increased and decreased, and the pulsation of an electromotive force waveform therefore can be reduced.
However, according to the invention described in Patent Document 1, since the distance between the rotor and the stator in areas between adjacent protruding portions becomes excessively large, torque ripple cannot be reduced sufficiently.
Patent Document 2 describes an invention for reducing the torque ripple. In Patent Document 2, in a cross section perpendicular to a central axis of rotation, a rotor has first protruding portions and, furthermore, second protruding portions formed on an outer peripheral face thereof, the first protruding portions each opposing the vicinity of the center of each permanent magnet and having an arc-shaped cross section protruding outward and the second protruding portions each opposing an area between permanent magnets and protruding outward. With the rotor having such a configuration, it is possible to reduce torque ripple while improving output torque.    Patent Document 1: JP 2002-95194A    Patent Document 2: JP 2005-354798A